In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, Long Term Evolution (LTE) has been under study (see, for example, Non-Patent Literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band for LTE specifications, which is 20 MHz, to approximately 100 MHz.
On the downlink in the LTE system (LTE system), the CRS (Common Reference Signal), which is a reference signal that is common between cells, is defined. This CRS is used for demodulation of data channel signals, and, in addition, used for downlink channel quality (CQI: Channel Quality Indicator) measurement for scheduling and adaptive control, and furthermore used for estimation of average downlink channel state (mobility measurement) for cell search and handover.
On the other hand, on the downlink of the LTE-advanced system (LTE-A system), in addition to this CRS, providing the CSI-RS (Channel State Information-Reference Signal) for dedicated use for CQI measurement, is under study. This CSI-RS supports CQI measurement for a plurality of cells by taking into account the transmission and reception of data channel signals by coordinated multiple point (CoMP). The CSI-RS is used for CQI measurement for adjacent cells, and, in this respect, differs from the CRS, which is used in CQI measurement for the serving cell alone.